This invention relates generally to reactors for performing chemical reactions, and more particularly to a reactor in which at least one of the chemical reactions is caused by electrolysis.
Generating products by electrolyzing a chemical compound into its constituent elements, one of which may be a gas, is known in the art. Typically, a direct current is applied across a pair of electrodes in contact with an electrolyte to cause decomposition of the electrolyte into one or more product gases.
Electrochemical reactors can be utilized for the production of various gases. For example, in the production of hydrogen gas, typically an electric current is passed between spaced electrodes in an aqueous electrolyte solution (e.g., water). Some fraction of water molecules ionize and the positively charged hydrogen ions migrate to the cathode electrode, while the negatively charged oxygen-containing ions-migrate to the anode electrode. The hydrogen ions undergo a reduction at the cathode, as they require electrons to neutralize their positive charges. This reduction produces bubbles of hydrogen gas, which rise to the surface of the aqueous electrolyte solution where they can be collected. Other gases, such as carbon dioxide and oxygen, for example, can also be produced by electrolysis, depending on the choice of electrodes and/or electrolyte solution.
Known electrolysis systems come in various shapes and sizes, and may have many different applications. For example, in U.S. Pat. No. 6,572,740, Rosenblum et al. describe an electrolytic cell using 0.15 ml to 100 L of an electrolytic solution, wherein the electrolytic cell can be used as a gas generator in a drug delivery device. Electrolysis systems can also be used in the microbial treatment of waste material. For example, in U.S. Pat. No. 3,992,268, Antos describes a method for treating waste materials comprising reacting a microorganism with a waste material which produces a carboxylic acid and subsequently electrolyzing the carboxylic acid product in an electrochemical cell, producing carbon dioxide.
German chemist Adolf Wilhelm Hermann Kolbe first demonstrated that the electrochemical oxidative decarboxylation of carboxylic acid salts leads to the synthesis of organic radicals which dimerize. This reaction is known as the Kolbe process, or the Kolbe reaction. A by-product produced during this synthesis reaction is carbon dioxide. By way of example, Law, Jr. et al. describes in U.S. Pat. No. 6,238,543 a method of performing the electrolytic coupling of carboxylic acids via the Kolbe reaction using a novel polymer electrolyte membrane reactor.
Research has indicated that the carbon dioxide produced during the Kolbe reaction is produced predominantly from the C1-position of small carboxylates, such as acetic acid. (See, for example, Wilson, C. T.; Lippencott, W. T., J. Am. Chem. Soc. 1956, 78, 4290-4294; Ross, S. D.; Finkelstein, M.; Petersen, R. C., J. Am. Chem. Soc. 1964, 86, 4139-4143; Belanger, G.; Lamarre, C.; Vijh, A. K., J. Electrochem. Soc. 1975, 122, 46-50). Thus, Kolbe electrolysis can be used to measure isotope enrichment of certain elements in isotopically enriched compounds. For example, Kolbe's electrolysis reaction has been used to measure isotope enrichment at certain carbon positions of carboxylic acids. According to this process, 13-carbon-enriched carboxylic acids, such as formic acid, acetic acid, and propanoic acid, are electrolyzed to produce carbon dioxide. This carbon dioxide can then be analyzed by a gas analyzer to determine the specific ratios of various carbon isotopes. Additionally, other isotopically enriched compounds, such as water, dicarboxylic acids, keto acids, and salts thereof may be analyzed in this manner. This technique and apparatuses thereto are described in May et al., Vacuum Electrolysis Reactor Technique for Quantitation of 13-Carbon Isotope Enrichment at the C1-Position of Formic Acid and Acetic Acid, Anal. Chem. 2004, 76, 5313-5318, which is hereby incorporated by reference in its entirety.
It is important in the analysis of carbon isotope ratios through carbon dioxide measurement to provide gas samples that are not substantially contaminated with other carbon isotopes, such as predominantly occurring 12-carbon that may result in inaccurate measurements. Additionally, isotopic-carbon-enriched carboxylic acids can be extremely expensive, so it is typically necessary to use small amounts for various analytical measurements. Further, once the carbon dioxide is produced through the Kolbe electrolysis reaction, it must be analyzed by some type of gas analyzer, such as a gas chromatograph and/or a mass spectrometer. Therefore, the gas must be easily removed or otherwise readily accessible for subsequent analysis without substantial loss or contamination.
It would be desirable, therefore, to provide an electrolysis system for the net production of carbon dioxide which is durable, transportable, requires only a small amount of electrolyte solution, and which prevents the decontamination of the reaction products through leaking or other source of contaminants.